1. Field of the Invention
This invention relates in general to apparatus and methods for spraying heavy viscous materials. In particular, the invention relates to the spraying of heavy viscous material such as aggregated materials which are difficult and expensive to handle and apply.
2. Description of the Prior Art
Heavy viscous materials such as aggregated materials have been applied by hand in the past. Attempts to apply the materials by spraying using hand held hopper guns or machines that employ rotor/stator pumps have met with limited success. The aggregated materials include gritty components which have a tendency to destroy many of the types of pumps that have been used to spray these materials. In the past, when the heavy aggregated material has been sprayed by this type of equipment, the machinery tends to break down, and is very costly to operate and maintain.
In the prior art, spray systems have been provided which include pressure pots or tanks through which a supply of material is forced out under air pressure. In the prior art spray systems problems arise when the material level nears the bottom of the pressure pot. At the point the pressurized air tends to push down through the material, through the tank's outlet port and out through the hose and spray gun. This causes objectionable spattering on the wall or other surface, and results in spoilage of the job.
Heavy viscous material is also difficult to clean out of the supply lines and hoses after the spraying operation. The conventional methods to clean the hoses include forcing the material out with water pressure. Cleaning elements such as sponges have also been used by forcing the sponges through the hose with water pressure. This method is not entirely satisfactory. Heavy viscous spray material is thick and tends to build up on the walls of the hose. Thus, the use of water pressure to force sponges through the hose is time consuming, and it takes as long as several minutes to push a sponge through a 50-foot hose. Normally the sponge must be pushed with the water pressure through the hose several times to thoroughly clean the material from the walls.